JP2007513382A - Reflected light coupler - Google Patents

Abstract

  The illumination system has individual light emitting diodes (LEDs) optically coupled to each optical fiber by a reflective coupler. At this time, the respective optical fibers may be bundled. The shape of the reflective coupler may be selected to increase the coupling efficiency between the LED and its optical fiber. The reflective coupler may be formed as an aperture passing through the sheet, having a first shape on the input side and a second shape different from the first shape on the second side. The reflective coupler may be formed as an aperture that passes through the body, wherein at least a first portion of the inner surface of the aperture follows a two-dimensional (2-D) surface and a second portion of the inner surface is three-dimensional (3-D). ) Follow the surface.

Description

  The present invention relates to an optical system, and more particularly to a coupler for coupling light from a light source that emits in a wide range to an object such as an optical fiber.

  The illumination system is used for various applications. In residential and industrial applications, it is often necessary to utilize light. Similarly, aircraft, marine and automotive applications often require a high intensity light beam for illumination. Conventional lighting systems have used filaments or arc lamps that are output by electricity. These illumination systems may include a focusing lens and / or a reflective surface to collect emitted light and direct it as a light beam to an intended object.

  However, in certain applications, it may be advantageous to remove the light source from environments where physical impact or sensitive electrical contact is undesirable or where space is limited. In response to such a need, an illumination system has been developed that guides light from a light source to a desired irradiation point using an optical waveguide. One current approach is to use one bright light source or series of light sources to illuminate the input end of an optical waveguide, such as a large diameter plastic fiber. In another approach, a single fiber may be replaced with a fiber bundle. These methods are generally inefficient because in some cases about 70% of the generated light is lost. In multi-fiber systems, some of the loss is due to the dark space between the fibers. The single optical waveguide approach lacks flexibility because an optical waveguide with a diameter large enough to capture the amount of light required for bright illumination applications becomes heavy.

  Some illumination systems use a laser as the light source, taking advantage of coherent light output and high coupling efficiency in the optical waveguide. However, laser light sources are expensive and typically generate light at a single wavelength, so they are not very useful when the requirement is for broadband illumination.

  Accordingly, there is a need for a lighting system that can efficiently supply high intensity illumination at a reasonable cost using a remote light source.

  One specific approach for building a high intensity lighting system is to couple light from individual light emitting diodes (LEDs) into respective optical fibers. Each optical fiber may then be bundled to form a remote lighting output. A reflective coupler between each LED and its respective optical fiber provides highly efficient optical coupling. In order to maintain high coupling efficiency between the LED and its optical fiber, the shape of the reflective coupler is important.

  One embodiment of the invention relates to a reflective coupler comprising a body having an aperture leading from a first side to a second side. The inner surface of the aperture is reflective. The first part of the internal reflection surface follows a two-dimensional (2-D) surface, and the second part of the internal reflection surface follows a three-dimensional (3-D) surface. The 2-D surface extends at least partially between the first side and the second side of the body.

  Another embodiment of the invention relates to an optical system comprising a first reflective coupler disposed substantially along a reflector axis. The first light source is disposed near the first side of the body for emitting light to the aperture. The first optical fiber has an entrance surface disposed near the second side of the body portion for receiving light passing through the aperture from the first light source. The reflective coupler is formed from a body having an aperture that leads from the first side to the second side. The inner surface of the aperture is reflective. The first part of the internal reflection surface follows a two-dimensional (2-D) surface, and the second part of the internal reflection surface follows a three-dimensional (3-D) surface. The 2-D surface extends at least partially between the first side and the second side of the body.

  Another embodiment of the invention relates to a reflective coupler comprising a sheet of material and having an aperture that leads from a first side of the sheet to a second side of the sheet. The first aperture edge on the first surface of the sheet has a first peripheral shape having a first number of sides, and the second aperture edge on the second surface of the sheet is the first A second peripheral portion having a second number of sides different from the number of sides. The aperture has an internal reflective surface extending between the first aperture edge and the second aperture edge.

  Another embodiment of the invention relates to an optical system comprising a first reflective coupler disposed substantially along a reflector axis. The reflective coupler is formed from a sheet of material having an aperture leading from the first side of the sheet to the second side of the sheet. The first aperture edge on the first surface of the sheet has a first peripheral shape having a first number of sides, and the second aperture edge on the second surface of the sheet is the first It has a second peripheral shape having a second number of sides different from the number of sides. The aperture has an internal reflective surface extending between the first aperture edge and the second aperture edge. The first light source is disposed in the vicinity of the first aperture edge. The first optical fiber having an entrance surface is disposed in the vicinity of the second aperture edge.

  The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The drawings and the following detailed description embody these embodiments in more detail.

  The invention will be more fully understood upon consideration of the following detailed description of various embodiments of the invention in conjunction with the accompanying drawings.

  While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. However, it should be understood that the invention is not limited to the specific embodiments described. On the contrary, it is intended to cover all modifications, alternatives, and variations encompassed within the spirit and scope of the invention as defined by the appended claims.

  The present invention is applicable to optical systems, and more particularly to light collection and management systems useful for illuminating objects with light from one or more light emitting diodes (LEDs).

  LEDs with higher output power are becoming more readily available, opening up new uses for LED lighting with white light. Among the applications that can be addressed using high power LEDs are projection and display systems, machine vision systems and camera / video applications, and even far-distance lighting systems such as automotive headlamps.

  Since LEDs typically emit light over a wide range of angles, one challenge for optical designers is in the direction of efficient collection of light generated by the LED and collection into a selected area of interest. . In some applications, the area of interest is an input to an optical waveguide, such as an optical fiber, so light may be used for remote illumination. For example, some light sources include one or more LEDs that emit light to each multimode optical fiber.

  An example of such a light illumination system 100 is schematically shown in the exploded view shown in FIG. The system comprises a plurality of LEDs 102 that are optically coupled to respective optical fibers 106 by respective reflective couplers 104 in a matched array. The LED 102 may be disposed on the substrate 103. The fibers 106 may be collected and grouped into one or more bundles 108 that carry the light to one or more illumination devices 110. The fiber 106 may be a multimode optical fiber. The LEDs 102 and the reflective coupler 104 may be housed in a housing 112, and the fibers 106 may be held in a spatial array near the respective coupler 104 and LED 102 using a fiber mounting plate 114. The system 100 may include a power source 116 that is coupled to supply power to the LEDs 102.

  A partial cross section of an embodiment of the assembled light source 200 is schematically illustrated in FIG. The light source 200 includes a base 202 that may be used as a heat sink. A thermally conductive layer 204 may be used to form a thermal bond between the array of LEDs 206 and the base 202. The plate 208 houses an array of reflective couplers 210 that couple the light 212 from the LEDs 206 to the respective array of optical fibers 214. The LEDs 206 are optically coupled to respective fibers 214 by respective reflective couplers 210. The reflective coupler 210 may be filled with air, or light with a higher refractive index than air, such as optical epoxy, to suppress the refractive index change at the interface of the LED 206 with the semiconductor material and thus reduce reflection losses. A permeable material may be included. The light transmissive material may partially fill the reflector 210 or may completely fill the reflective coupler 210 from the LED 206 to the fiber 214. Fiber 214 may be held in place relative to the array of reflective couplers 210 by fiber plate 216. The output ends of the fibers may be combined and used as a light source for illumination.

  The plate 208 may be shaped with an aperture therethrough to form the reflective coupler 210. The reflective surface of the reflective coupler may be formed using different techniques, for example by metal coating or dielectric thin film coating.

  At least some of the colors of the light 212 generated by the LED 206 may be converted to one or more different colors to cover a wider band of the visible spectrum. For example, if the LED 206 generates blue or UV light, the phosphor may be used to generate other color bands in the visible region of the spectrum, such as green, yellow and / or red light. The phosphor may be included in the upper part of the LED 206, may be provided at the entrance to the fiber, or may be provided elsewhere. One or more wavelength selective reflectors may be used to improve color conversion efficiency. The use of phosphors to convert the color of the light 212 emitted by the LED 206 is described in US Provisional Application Nos. 60 / 443,235, 60/443, filed Jan. 27, 2003, respectively. No. 274 and 60 / 443,232, the following patents filed on Dec. 2, 2003, US Patent Application No. 10 / entitled “Phosphor Based Light Sources Having a Polymeric Long Pass Reflector” In addition, U.S. Patent Application No. 726,997 and U.S. Patent Application No. 10 / 727,072 entitled "Phosphor Based Light Sources Having a Non-Planar Long Pass Reflector". It has been described.

  The reflective coupler for coupling light from the LED to the fiber may use the shape of a compound parabolic concentrator (CPC). This type of reflector initially collects solar radiation as described, for example, by Welford and Winston, "High Collection Nonimaging Optics", Academic Press, San Diego, CA, 1989. Developed to be. CPCs are known to be efficient reflective concentrators where the possible collection ratio, i.e. the ratio of input area to output area, is very close to maximum.

  However, there are several disadvantages to using CPC as a reflective coupler in LED-based lighting systems. For example, CPC is somewhat limited in its ability to efficiently couple light to an object having a shape different from the shape of the light source. This is a problem because many LEDs have square or rectangular light emitting areas and optical fibers generally have a circular cross section. Even when the source and object ranges are the same, CPC is inefficient when coupling from a square light source to a circular fiber object. From simple physical constraints, it can be seen that efficient coupling by CPC requires that the square or rectangular light source range be significantly smaller than the fiber range. Since the CPC contour may be such that the diameter of the central portion of the CPC is larger than the diameter at both ends, another problem is that it makes mass production of reflectors using molding techniques difficult, if not impossible. is there.

  Furthermore, a high concentration ratio is not necessarily a useful performance factor for a reflector that is to couple light from an LED into a fiber having an aperture that is larger than the LED's emission aperture. Even more important is the ability to couple most of the light into useful modes of the optical fiber. Therefore, the usefulness of CPC in coupling light from an LED to an optical fiber object is limited.

A uniform diffuse reflection surface light emitter is a light emitter that emits light equally at all angles. Although not exactly a uniform diffuse reflector, an LED is essentially a substantially uniform diffuse reflector, and since it is at least a hemisphere from which light is emitted, it is uniform in light of the design of a coupler for coupling light into a fiber. It is convenient to consider a diffuse reflective surface light source. Now, one aspect of the design of an optical coupler for coupling light into an optical fiber will be discussed with reference to FIG. Since the uniform diffuse reflection surface light source 302 has a side length “a”, the light source 302 has a light emitting region having a square shape with a diagonal length of a√2. The fiber 304 has a circular incident aperture 306 with a diameter d. The light source 302 and the incident aperture 306 are on the axis 308. It is assumed that light that is directly incident on the incident aperture 306 is incident within a light receiving angle θ of the fiber defined by the numerical aperture (NA) of the fiber. For air, NA is the sine of the acceptance angle. Under this constraint, the minimum distance L _min between the light source and the fiber is given by:
L _min = (a√2 + d) / (2 tan θ) (1)

An example value for a, d, and θ is a = 300 μm, d = 600 μm, NA (in air) = sin θ = 0.48, and in this example, L _min is about 936 μm. Light that is not directly incident on the incident aperture 306 may be reflected by another surface, that is, the surface of the reflective coupler. Furthermore, in order to increase the amount of light that is efficiently coupled to the fiber, the reflecting surface is oriented to reduce the angle of the reflected light with respect to the reflector axis, so that more light is received by the fiber's receiving cone. Fits in. This means that a relatively acute angle is desirable. Therefore, the shape of the reflective coupler is important in order to maintain high coupling efficiency between the LED and the optical fiber. One example of a reflective surface for reflectively coupling light from an LED to an optical fiber is described in US patent application Ser. No. 10/10, entitled “ILLUMINATION SYSTEM USING A PLURALITY OF LIGHT SOURCES” filed on Dec. 2, 2003. No. 726,222 (U.S. Patent Publication No. 2004-0149998-A1). In detail, the contour of the reflective coupler is calculated to be close to a paraboloid shape and is accurately represented by a quartic equation.

  In order to describe the different surface shapes used in the following description of the reflective coupler, it is useful to define several terms. The term “two-dimensional plane” or “2-D plane” refers to the shape of a cross section whose plane has a radius of curvature in at most one plane, for example the xz plane or the yz plane, perpendicular to its axis. Or it means that it can extend along one axis without changing its size. Examples of the 2-D surface include a flat surface (the radius of curvature is infinite), a cylindrical surface, and an aspherical column surface. FIG. 4A shows a cylindrical surface 402. Examples of the aspherical cylindrical surface include a parabolic cylindrical surface, an elliptical cylindrical surface, and a hyperbolic cylindrical surface. A parabolic column surface 404 is schematically illustrated in FIG. 4B and an elliptical column surface 406 is schematically illustrated in FIG. 4C. In each of the embodiments shown in FIGS. 4A to 4C, the surfaces 402 to 406 are column surfaces centered on an axis parallel to the x axis. Also, the surfaces 402-406 can extend along the x-axis without changing the shape or size of the respective circle, parabola or ellipse.

  A three-dimensional plane or 3-D plane is a plane of rotation or a plane having a radius of curvature in two or more planes, for example, having a radius of curvature in both the xz plane and the yz plane. Some examples of rotating surfaces are cones, parabolas, ellipsoids and hyperboloids. Examples of a surface having a radius of curvature in two or more planes include a spherical surface and a toroidal surface. In the following description, when it is indicated that the reflecting surface follows a specific 2-D surface or 3-D surface, the reflecting surface only needs to follow a part of the specific 2-D surface or 3-D surface. Please understand.

  One approach for designing a reflective coupler will now be described with reference to FIGS. 5A-5K. FIG. 5A schematically illustrates an input aperture edge 502 that corresponds to a square light source, such as a light emitting area of an LED. The output aperture edge 504 corresponds to the incident aperture of the optical fiber. Aperture edges 502 and 504 form the basic shape of the input to and output from the reflective coupler. The axis 506 is referred to as the reflector axis and passes between the center of the input aperture edge 502 and the center of the output aperture edge 504. The reflector axis 506 is parallel to the z axis.

  The shape of the input to the reflective coupler has a different number of sides with respect to the shape of the output. In the embodiment shown above, the peripheral shape of the input aperture edge 502 is square, has four sides, and the sides are defined as straight portions. The peripheral shape of the output aperture edge 504 is circular. A circle is generally understood to have an infinite number of sides. Accordingly, the input aperture edge 502 defines a peripheral shape having a plurality of sides different from the number of sides of the output aperture edge 504.

  One or more 2-D planes are configured relative to the input aperture edge 502, as shown in FIGS. 5B and 5C. In this particular embodiment, the 2-D plane conforms to a parabolic column surface. A parabola 508 is drawn in the yz plane and intersects the upper and lower sides of the input aperture edge 502 and the upper and lower sides of the output aperture edge 504. The solid line portion of the parabola 508 includes a portion of the aspherical cylindrical surface that is aligned with the x-axis, as described below with reference to FIG. 5C. The broken line portion of the parabola 508 is truncated, and is shown only to show that a single parabola is used in this embodiment.

  FIG. 5C shows the parabola 508 of FIG. 5B after extending in the + x and −x directions to form parabolic pillar surfaces 510a and 510b. Surfaces 510a and 510b are opposing aspheric surfaces with power (curvature) in only one direction. That is, the radii of curvature of the surfaces 510a and 510b are in the yz plane.

  Here, another 2-D plane configuration will be described with reference to FIGS. 5D and 5E. In FIG. 5D, a parabola 512 is drawn in the xz plane and intersects the right and left centers of the input aperture edge 502 and the right and left sides of the output aperture edge 504. The solid line portion of the parabola 512 corresponds to a part of the aspherical column surface shown in FIG. 5E, and the broken line part of the parabola 512 is shown to show that one parabola is used. The solid line portion of the parabola 512 extends in the + y direction and the -y direction to form a pair of opposing aspheric surfaces 514a and 514b.

  FIG. 5F schematically shows the 2-D surfaces 510a, 510b, 514a and 514b alternately arranged with respect to each other, and FIG. 5G shows the 2-D surfaces 510a, 510b, FIG. 5F with portions away from the intersections removed. 514a and 514b are shown schematically. Surfaces 510a, 510b, 514a and 514b accurately accommodate the desired input aperture edge 502 corresponding to a square light source. However, at the opposite end, the square output 516 does not closely match the circular output edge 504. If the reflective coupler is to be formed only from the 2-D surfaces 510a, 510b, 514a and 514b, the circular output edge 504 is a square output 516 of the 2-D surfaces 510a, 510b, 514a and 514b. A considerable amount of light will be lost in the region 518 that does not match.

  Therefore, by using only the 2-D plane, the input edge does not match a shape having a straight side, and the output edge does not become a reflecting surface that matches a shape having a circular shape.

  Instead, consider another surface that matches the circular aperture of the output edge 504. This plane is a 3-D plane, specifically a plane of rotation about the reflector axis 506, as described herein with reference to FIGS. 5H and 5I. In the illustrated embodiment, the parabola 520 matches the circular output aperture edge 504 and matches the portion of the input aperture edge 502 furthest from the axis 506, ie, the corner of the input aperture edge 502. A rotation surface 522 is formed by rotation of a parabola around the axis 506. The face 522 does not hit the interior of the area drawn by the input aperture edge 502.

  There are drawbacks to using either a 2-D plane only set or a 3-D plane only set as the reflective surface for a reflective coupler to couple between the LED and the fiber. As described above with respect to FIG. 5G, the use of the 2-D plane results in a portion 518 that does not couple to the fiber, so that light is lost. Thus, the use of only the 2-D plane results in reduced coupling to the fiber.

  The use of only a rotating surface also results in reduced light coupling to the fiber for reasons described herein with reference to FIG. Consider the following comparison of the reflection of light 604 by reflective surfaces 626 and 628. One reflective surface 626 corresponds to the line 526 on the parabolic surface 522 and represents a parabolic reflective surface 522. The other reflective surface 628 corresponds to a curve 528 that extends from the output aperture edge 504 to the center of the upper edge of the square input aperture edge 502. This reflecting surface corresponds to a parabolic column surface such as the surface 510a.

  Light 604 is incident on each reflective surface 626 and 628. The light reflected by the surface 628 propagates at an angle θ1 with respect to the optical axis 506 as light 638. The light reflected by the surface 626 propagates as light 636 with respect to the optical axis 506 at an angle θ2. Since the surface 628 has a sharper angle θ 1 <θ 2, the light 638 is more likely to enter the fiber than the light 636 within the fiber receiving angle. Thus, the sharper angle formed by the reflective surface 628 results in greater coupling to the fiber, so the use of a 2-D surface at a location at least near the input of the reflective coupler will allow the light coupled into the fiber. Increase the amount.

  One approach to ensuring high efficiency when coupling light from an LED to a fiber is to use a reflective surface that combines both 2-D and 3-D surfaces. This will be described with reference to FIGS. 5J and 5K. FIG. 5J shows a composite with all faces 510a, 510b, 514a, 514b and 522 extending between the input aperture edge 502 and the output aperture edge 504. FIG. When light is emitted from the light source at a large angle with respect to the optical axis 506, the light preferentially strikes the 2-D plane that forms a sharper angle with respect to the plane of rotation, so that a larger portion of the reflected light is more of the Fits in NA. At a point closer to the output of the reflective coupler, there is a transition from the 2-D plane to the 3-D plane that matches the shape of the fiber. FIG. 5K schematically shows a “truncated” version of the reflective coupler shown in FIG. 5J. The cut-off version includes 2-D surfaces 510a, 510b, 514a and 514b closer to the optical axis 506 than the 3-D surface 522, and 3 closer to the optical axis 506 than the 2-D surfaces 510a, 510b, 514a and 514b. -Only the portion of the D surface 522 is included.

  To help understand the shape of the reflective surface, cross-sectional views of the reflective coupler are provided in FIGS. 7A-7D. 7A-7C show cross-sectional views of the interior of the reflective coupler as viewed along axis 506. Therefore, the plane of the portion shown in FIGS. 7A to 7C is parallel to the xy plane. FIG. 7A shows a cross-section at the input aperture edge 502 of the reflective coupler. At the input aperture edge, all the 2-D planes are closer to the optical axis 506 than the rotation plane 522, so the cross-sectional shape matches the 2-D planes 510a, 510b, 514a and 514b. FIG. 7B shows a cross section of the reflective coupler at a point that is about halfway between the input aperture edge 502 and the output aperture edge 504. In this respect, the 3-D surface 522 is closer to the axis 506 than the intersection between the 2-D surfaces 510a, 510b, 514a, and 514b, so that the reflective coupler fits the 3-D surface 522 at "corners". The central flat portions of the 2-D surfaces 510a, 510b, 514a, and 514b remain closer to the axis 506 in the + x, -x, + y, and -y directions. FIG. 7C shows a cross section of the reflective coupler near the output aperture edge 504. The widths of the flat portions 510a, 510b, 514a and 514b are reduced and the range of the 3-D surface 522 is increased. At the output aperture edge, the cross section of the reflective coupler includes only the 3-D surface 522.

  The 2-D surfaces 510a, 510b, 514a, and 514b may be expressed as “alternately arranged” with the 3-D surface 522. The term “alternately arranged” means that at least one section of the cross section follows the 2-D plane with respect to at least one cross section of the reflective coupler taken perpendicular to the reflector axis. Means to follow the 3-D plane. The cross sections shown in FIGS. 7B and 7C indicate that the cross sections are alternately arranged because they show portions that follow both the 2-D plane and the 3-D plane.

  A cross-sectional view of reflective coupler 700 perpendicular to axis 506 is shown schematically in FIG. 7D. This figure also shows that the reflective coupler 700 is formed as an aperture 708 through the body 710 when the input aperture edge 502 matches the LED emitter 702 and the output aperture edge 504 matches the optical fiber 704. It shows that you may be. The optical fiber 704 has a cladding 705. The body 710 may have only one aperture 708 extending therethrough and may extend in the x and y directions like a sheet. The body 710 may have a plurality of apertures, such as an aperture 708 that extends from one side to the other.

  The reflective surface of the reflective coupler 700 has different parts that match the 2-D and 3-D planes described above. It can be seen that the 2-D surfaces 510a and 510b are at the top and bottom of the reflective coupler 700, respectively, and the 2-D surface 514b is behind the aperture in this view. Line 720 represents the boundary between 2-D surface 514b and 3-D surface 522. The reflective surface is characterized by a 3-D surface 522 progressively toward the output aperture edge 504.

  The reflective coupler 700 has different shapes at its input and output, and is formed from a 3-D surface such as a rotating surface combined with a plurality of 2-D surfaces. In the example described with respect to FIGS. 5A-5K, it was assumed that the 2-D plane was a parabolic column surface and the 3-D plane was a parabolic rotation surface. The present invention is not limited to using only surfaces that conform to these shapes, and other types of surfaces may be used. For example, the 2-D plane may be planar, cylindrical or elliptical, or may have some other 2-D shape. Also, the 3-D surface may be conical, elliptical, or assume some other 3-D shape.

  Further, although the input aperture edge has been described as square in the above-described embodiments, it will be appreciated that the present invention is not intended to be limited to a square input aperture edge. An input aperture edge with four other sides may be used, for example, the input aperture edge may be rectangular, or some other quadrilateral shape may be employed. The input aperture edge is set based on the desired shape for the input section. For the purposes of this description, the term rectangular includes a shape that is square. The input aperture edge may also take on different shapes with straight sides. For example, the input aperture edge may be a triangle, pentagon, hexagon, or the like. The 2-D surface may be formed to match each of the straight sides of the input aperture edge. For example, if the input aperture edge is a triangle, the 3-D surface may be a combination of three 2-D surfaces.

  A reflective coupler having a surface following a 3-D surface, such as a plurality of 2-D surfaces and a rotating surface, is referred to herein as a 2D-3D composite reflector.

  The performance of reflective couplers with different shapes was calculated. In either case, the light source was assumed to be a 300 μm square uniform diffuse reflector surface emitter located 936 μm from the fiber entrance surface. The fiber core diameter was assumed to be 600 μm and its NA was 0.48. The internal reflection surface of the reflector was assumed to be covered with silver, and Fresnel reflection was considered at the near and far edges of the fiber. The calculated coupling efficiency results are shown in Table I. Since the source range is larger than the fiber range, it was not possible to achieve 100% coupling efficiency using this model.

  The first two geometries, a) a simple cone and b) a paraboloid represented a reflector formed using only the 3-D plane. A simple cone was a cone with circular input and output apertures. The output aperture matched the fiber diameter and the input aperture had a diameter equal to the diagonal of the light source. The paraboloid reflector had a paraboloid of rotation and a circular input and output aperture. The output aperture matched the fiber diameter and the input aperture had a diameter equal to the diagonal of the light source.

  c) Reflectors formed using intersecting parabolic cylinder surfaces are reflectors formed only from 2-D planes, eg, surfaces 510a, 510b, 514a and 514b as shown in FIG. 5G. Represents a suitable reflector.

  The last two geometries d) and e) are examples of 2D-3D composite reflectors. Example d) was assumed to be formed using four planar 2-D surfaces forming a truncated pyramid shape alternating with simple cones as 3-D surfaces. Example e) was assumed, for example, as shown in FIG. 5K, that the 2-D surface is a parabolic column surface and the rotating surface is a parabolic surface. As can be seen from the calculation results, the coupling efficiency for the 2D-3D composite reflector is significantly higher than the coupling efficiency of the simple 3-D reflectors (reflectors a) and b)), and is a composite 2-D reflector (reflector). higher than the coupling efficiency of c)).

  Until now, it has been assumed that the light source is a planar uniform diffuse reflector. However, this is not necessarily the case and the light source may have a more complex shape than a simple plane. For example, certain high powers such as the “XBright®” series of silicon carbide (SiC) LEDs manufactured by Cree Inc. of North Carolina. The LED has a facet shape as schematically shown in FIG. The LED 800 has an upper surface 802 and a slope 804, all of which can emit light. Bond pad 806 may be positioned on top surface 802 to facilitate electrical connection. Most of the light output from the LED 800 is emitted from the slope 804, and part of the light is emitted from the upper surface 802. An LED axis 808 is also shown.

  The complex LED geometry as shown in FIG. 8 presents a cumbersome problem in the design of reflectors for the efficiency of propagating light emitted into objects having different shapes, such as fibers. The slope tends to cast more light on the side far from the LED axis. A further consideration is that the LED body is generally composed of a semiconductor material having a relatively high refractive index. For example, SiC has a refractive index in the range of 2.6 to 2.7, and gallium nitride (GaN) has a refractive index of about 2.4. These relatively high values of refractive index cause most of the light incident on the inner surface of the LED itself to be reflected and subsequently scattered, absorbed or otherwise lost. This effect may be partially mitigated by encapsulating the LED in a material having a higher refractive index than air, such as an optical epoxy having a refractive index of about 1.6. The resulting change in refractive index at the surface of the semiconductor LED die reduces the Fresnel reflection loss, thus allowing for higher extraction of light generated from the LED semiconductor die into the LED.

  When the encapsulating material extends to the input end face of the fiber, the angle of incidence at the fiber end face that allows coupling to the fiber is proportionally reduced. For example, if the fiber NA in air is 0.48 and the area between the LED and the fiber is filled with n = 1.56 epoxy, the allowable angle of incidence at the fiber end face is 28.7. Decrease from ° to 17.9 °. Thus, light that is coupled into the fiber at an angle greater than 17.9 ° is not guided into the fiber and is lost in the fiber cladding. Therefore, it is important to shape the reflective coupler so that as much light as possible is directed to the fiber within this reduced cone angle.

  In the 2D-3D composite reflector example described above, the opposing 2-D surfaces, such as surfaces 510a and 510b shown in FIG. 5K, matched a parabolic column surface whose axis coincided with the reflector axis 506. This is not necessarily true, and the axis of the parabolic column does not have to coincide with the reflector axis, and need not be parallel to the reflector axis. Furthermore, the opposing 2-D surfaces may be matched to surfaces having different axes. For example, surface 510a may be formed with respect to a first axis and surface 510b may be formed with respect to a second axis. This is shown in FIG. 9 and schematically illustrates a reflective coupler 900 for coupling light from an LED 930 having a shape similar to the LED of FIG. 8 to an optical fiber core 932. The fiber core 932 may be surrounded by a cladding 934.

  The reflective coupler 900 may be formed as an aperture 901 that passes through the main body 903. The aperture 901 has a plurality of 2-D surfaces with surfaces 910a, 910b and 914b and a reflective wall following the rotating surface 922. Surfaces 910a and 910b extend in and out of the plane of the figure in a manner similar to surfaces 510a and 510b of FIG. A line 920 indicates a boundary between the 2-D surface 914b and the 3-D surface 922. The 2-D surface comprising the surfaces 910a, 910b and 914b forms an incident aperture edge 902 that closely follows the shape of the LED 930. In this particular embodiment, each 2-D surface follows a parabolic reflection surface formed about a respective 2-D surface axis that is offset from the reflector axis 906. For example, the 2-D surface 910a follows a parabolic 2-D surface formed around a 2-D surface axis 916a. Similarly, the 2-D surface 910b follows a 2-D surface formed around the 2-D surface axis 916b. It will be appreciated that the 2-D surface 914b and any other existing 2-D surface may also be formed about a respective 2-D surface axis (not shown).

  The 2-D surface axes 916a and 916b do not need to coincide with the reflector axis 906, and may be shifted with respect to the reflector axis 906. The 2-D surface axes 916a and 916b may be parallel to the reflector axis 906, but may not be parallel. The 2-D surface axes 916a and 916b may be positioned so as to pass through the center of the inclined surface 938 of the LED 930, for example. Such an arrangement may be particularly useful when the ramp 938 emits most of the light output from the LED 930. Furthermore, when the 2-D plane has a focal point, the focal point may be disposed at or near the center of the inclined surface 938. Examples of the 2-D plane having a focal point include a paraboloid and an ellipsoid. Placing the focal point near the center of the surface emitting most of the light is advantageous in that the portion of emitted light directed toward the fiber core 932 is increased in a direction substantially parallel to the reflector axis 906.

  In the case of light emanating from the beveled facet 938 in a direction that is not directly incident on the end of the fiber core 932, the 2-D reflectors 910a, 910b and any other 2-D surfaces are reflected and Because the light is partially collimated towards the core 932, the portion of the emitted light that enters the fiber core 932 in the fiber NA increases. Light is also emitted from the planar end 940 of the LED 930. Part of this light is directly incident on the input to the fiber 932, and part of the light is reflected from the reflector 900 and then enters the input of the fiber.

  The coupling efficiency of light from an LED with a shaped die as shown in FIG. 8 was compared to that of a reflective coupler with a different geometry. In particular, the coupling efficiency of a tapered conical reflector adapted to two conical reflectors joined end to end along the axis of the reflective coupler results in an offset 2-D paraboloid and paraboloid 3-D. It was compared with the coupling efficiency of a 2D-3D composite reflector as shown in FIG. In either case, the reflective coupler was assumed to be filled with epoxy (n˜1.56) and index matched to the fiber. The amount of light coupled from the LED to the fiber using a tapered conical reflective coupler was normalized to 1. In comparison, the normalized amount of light coupled to the fiber using the 2D-3D composite reflector 900 was calculated to be about 1.7. In other words, the 2D-3D composite reflective coupler 900 was 70% more efficient than the tapered cone reflector in coupling light into the fiber.

  The present invention should not be construed as limited to the particular embodiments described above, but should be construed as encompassing all aspects of the invention as fully set forth in the appended claims. It is. Various modifications, equivalent methods, and various structures that may be applicable to the present invention will be readily apparent to those of skill in the art to which the present invention relates upon review of this specification. The claims are intended to cover such modifications and devices.

FIG. 2 shows an exploded view of an embodiment of an illumination system according to the principles of the present invention. 2 schematically illustrates a cross section of an assembly of the illumination system shown in FIG. 1 in accordance with the principles of the present invention. 1 schematically illustrates a model element for coupling light from a uniform diffuse reflecting surface light source to an optical fiber. Fig. 2 schematically shows various two-dimensional (2-D) planes. Fig. 2 schematically shows various two-dimensional (2-D) planes. Fig. 2 schematically shows various two-dimensional (2-D) planes. 1 schematically illustrates the configuration of an embodiment of a reflective coupler that combines a 2-D surface with a three-dimensional (3-D) surface according to the principles of the present invention; 1 schematically illustrates the configuration of an embodiment of a reflective coupler that combines a 2-D surface with a three-dimensional (3-D) surface according to the principles of the present invention; 1 schematically illustrates the configuration of an embodiment of a reflective coupler that combines a 2-D surface with a three-dimensional (3-D) surface according to the principles of the present invention; 1 schematically illustrates the configuration of an embodiment of a reflective coupler that combines a 2-D surface with a three-dimensional (3-D) surface according to the principles of the present invention; 1 schematically illustrates the configuration of an embodiment of a reflective coupler that combines a 2-D surface with a three-dimensional (3-D) surface according to the principles of the present invention; 1 schematically illustrates the configuration of an embodiment of a reflective coupler that combines a 2-D surface with a three-dimensional (3-D) surface according to the principles of the present invention; 1 schematically illustrates the configuration of an embodiment of a reflective coupler that combines a 2-D surface with a three-dimensional (3-D) surface according to the principles of the present invention; 1 schematically illustrates the configuration of an embodiment of a reflective coupler that combines a 2-D surface with a three-dimensional (3-D) surface according to the principles of the present invention; 1 schematically illustrates the configuration of an embodiment of a reflective coupler that combines a 2-D surface with a three-dimensional (3-D) surface according to the principles of the present invention; 1 schematically illustrates the configuration of an embodiment of a reflective coupler that combines a 2-D surface with a three-dimensional (3-D) surface according to the principles of the present invention; 1 schematically illustrates the configuration of an embodiment of a reflective coupler that combines a 2-D surface with a three-dimensional (3-D) surface according to the principles of the present invention; Figure 3 schematically shows reflections from two different surfaces into a reflective coupler. 5B schematically illustrates various cross sections of the reflective coupler illustrated in FIG. 5K. FIG. 5B schematically illustrates various cross sections of the reflective coupler illustrated in FIG. 5K. FIG. 5B schematically illustrates various cross sections of the reflective coupler illustrated in FIG. 5K. FIG. 5B schematically illustrates various cross sections of the reflective coupler illustrated in FIG. 5K. FIG. 1 schematically illustrates an LED having a complex shaped die; Fig. 6 schematically illustrates another embodiment of a reflective coupler that combines a 2-D surface with a 3-D surface according to the principles of the present invention.

Claims (44)

  A reflective coupler comprising a body having an aperture leading from a first side to a second side, wherein the inner surface of the aperture is reflective and the first portion of the inner surface is two-dimensional (2-D ) Surface, the second portion of the internal reflecting surface follows a three-dimensional (3-D) surface, and the 2-D surface is at least between the first side and the second side of the body portion. A partially extending reflective coupler.   The coupling according to claim 1, wherein the first portion is disposed near the first side of the body portion and the second portion is disposed near the second side of the body portion. vessel.   The coupler of claim 1, wherein the aperture defines a first aperture edge on the first side of the body, and the first aperture edge is rectangular.   The coupler of claim 1, wherein the aperture defines a second aperture edge on the second side of the body, and the second aperture edge is circular.   The coupler according to claim 1, wherein the 2-D surface is an aspherical column surface.   6. The coupler of claim 5, wherein the reflective surface near the first aperture edge substantially follows two intersecting aspheric cylindrical surfaces.   A reflector axis is defined in the longitudinal direction along the center of the aperture between the first side and the second side, and the aspherical column surface is formed around the reflector axis. The coupler according to claim 6.   The coupler according to claim 6, wherein the aspherical column surface is a parabolic column surface.   A reflector axis is defined longitudinally along the center of the aperture between the first side and the second side, and the 2-D plane comprises a plane formed with respect to a 2-D plane axis. The coupler of claim 1, wherein the coupler is a surface.   The coupler according to claim 9, wherein the 2-D plane axis coincides with the reflector axis.   The coupler according to claim 9, wherein the 2-D plane axis does not coincide with the reflector axis.   Further comprising a light emitting diode LED disposed on the first side of the body for emitting light to the aperture, the LED having a first light emitting surface that is not perpendicular to the reflector axis; The coupler of claim 11, wherein the 2-D plane axis passes through the first light emitting surface.   The coupler of claim 12, wherein the 2-D plane defines a focal point on the 2-D plane axis, and the focal point is positioned on the first light emitting surface.   The coupler of claim 1, wherein the aperture defines a second aperture edge on the second side of the body portion, the second aperture edge substantially following the 3-D plane.   The coupler according to claim 1, wherein the 3-D surface is a rotating surface.   A reflector axis is defined in a longitudinal direction along a center of the aperture between the first side and the second side, and the rotation surface is a rotation surface centered on the reflector axis. Item 16. The coupler according to Item 15.   The coupler of claim 15, wherein the rotating surface is a paraboloid.   The coupling of claim 1, wherein the reflective surface substantially follows four aspherical cylindrical surfaces near the first side and the reflective surface substantially follows a rotating surface near the second side. vessel.   The coupler according to claim 1, wherein the 2-D plane and the 3-D plane are alternately arranged. A first reflective coupler formed from a body portion having an aperture disposed substantially along the reflector axis and leading from the first side to the second side, wherein the inner surface of the aperture is reflective; At least a first portion of the internal reflection surface follows a two-dimensional (2-D) surface, at least a second portion of the internal reflection surface follows a three-dimensional (3-D) surface, and the 2-D surface is the main body. A first reflective coupler extending at least partially between the first side and the second side of a section;
A first light source disposed near the first side of the body portion for emitting light to the aperture;
An optical system including a first optical fiber having an incident surface disposed in the vicinity of the second side of the main body for receiving light passing through the aperture from the first light source.   21. The system of claim 20, wherein the light source is a light emitting diode.   A plurality of light sources for directing light to a plurality of respective optical fibers using a plurality of respective reflective couplers, the plurality of light sources comprising the first light source, and the plurality of optical fibers comprising the first light source; 21. The system of claim 20, comprising an optical fiber, wherein the plurality of reflective couplers comprises the first reflective coupler.   23. The system of claim 22, wherein the light sources are arranged in an array and the reflective coupler and optical fiber are arranged in respective arrays that match the light source array.   23. The system of claim 22, wherein the reflective coupler is formed of a sheet of material, and the material of the sheet comprises the body.   23. The system of claim 22, wherein the fibers of the plurality of fibers are combined and have an output at a lighting device.   23. The system of claim 22, further comprising a power source coupled to supply power to the plurality of light sources.   A reflective coupler comprising a sheet of material having an aperture leading from a first side of the sheet to a second side of the sheet, the first aperture edge at the first side of the sheet being a first A first peripheral shape having a number of sides, a second aperture edge on the second surface of the sheet defining a second peripheral shape having a second number of sides, the first The number of sides is different from the second number of sides and the aperture has a reflective coupler having an internal reflective surface extending between the first aperture edge and the second aperture edge .   28. The coupler of claim 27, wherein the first peripheral shape is rectangular and the second peripheral shape is circular.   28. The coupler of claim 27, wherein the first portion of the internal reflective surface follows a 2-D surface and the second portion of the internal reflective surface follows a 3-D surface.   The first peripheral shape includes a straight side, the internal reflection surface in the vicinity of the first aperture edge follows a 2-D surface, and each 2-D surface corresponds to each of the first peripheral edges. 30. The coupler of claim 29, terminating in a straight side.   31. The coupler of claim 30, wherein the 2-D surface comprises at least one pair of opposing 2-D surfaces that conform to an aspheric cylindrical surface.   32. The coupler of claim 31, wherein the aspherical column surface is a parabolic column surface.   A reflector axis is defined between the first side and the second side of the column surface along the center of the aperture, and at least one of the 2-D planes is relative to a 2-D plane axis. 30. The coupler of claim 29, wherein the coupler is formed.   The coupler of claim 33, wherein the 2-D plane axis coincides with the reflector axis.   The coupler of claim 33, wherein the 2-D plane axis does not coincide with the reflector axis.   30. The coupler of claim 29, wherein the second peripheral shape is circular and the internal reflective surface near the second aperture edge substantially follows a plane of rotation.   37. The coupler of claim 36, wherein the rotating surface is a paraboloid.   30. The coupler of claim 29, wherein the 2-D plane and the 3-D plane are alternately arranged. A first reflective coupler formed from a sheet of material disposed substantially along the reflector axis and having an aperture leading from a first side of the sheet to a second side of the sheet, the first of the sheets The first aperture edge on one surface defines a first peripheral shape having a first number of sides, and the second aperture edge on the second surface of the sheet is a second number of sides And the first number of sides is different from the second number of sides, and the aperture is defined between the first aperture edge and the second aperture edge. A first reflective coupler having an internal reflective surface extending therebetween;
A first light source disposed in the vicinity of the first aperture edge;
And a first optical fiber having an incident surface disposed in the vicinity of the second aperture edge.   40. The system of claim 39, wherein the light source is a light emitting diode.   A plurality of light sources for directing light to a plurality of respective optical fibers using a plurality of respective reflective couplers, the plurality of light sources comprising the first light source, and the plurality of optical fibers comprising the first light source; 40. The system of claim 39, comprising an optical fiber, wherein the plurality of reflective couplers comprises the first reflective coupler.   42. The system of claim 41, wherein the light sources are arranged in an array and the reflective coupler and optical fiber are arranged in a respective array that matches the light source array.   42. The system of claim 41, wherein the fibers of the plurality of fibers are combined and have an output at a lighting device.   42. The system of claim 41, further comprising a power source coupled to supply power to the plurality of light sources.

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